In the case of adopting a constant amplitude transmission signal by GMSK (Gaussian Minimum Shift Keying) modulation, and so forth, for mobile communications such as a cellular telephone, and so forth, much use is being made of an offset PLL (Phase Locked Loop) in a transmission circuit. With the offset PLL, a modulation signal is converted into one at a transmission frequency by applying modulation to a voltage-controlled oscillator as described in, for example, “RF Transmitter Architectures and Circuits” by Behzard Razavi, “IEEE 1999 Custom Integrated Circuits Conference” papers, 1999, pp. 197-204.
Further, as an example of a configuration of a transmitter for a conventional dual mode terminal adopting a constant amplitude modulation method by the GMSK modulation, and a nonconstant amplitude modulation method by an 8 PSK (Phase Shift Keying) modulation, there is cited an example of a configuration provided with a phase control loop (phase feedback loop) for controlling a phase of an output signal of a voltage-controlled oscillator by feedback, and an envelope feedback loop (amplitude control loop) for controlling a gain of a power amplifier for amplifying the output signal by feedback (refer to, for example, JP-A No. 7443/2004).